iOS: Checkmark, our favorite app for creating location-based reminders on iOS, is available for free today only in an "end of the world sale."

Apple's built-in Reminders app can handle location-based tasks, but it's cumbersome to actually create a new one. Checkmark is simple, and it only takes a few taps to do it. You can add favorite locations to the app, and then create reminders so when you arrive there you'll remember what you need to do. This is great for when you need to pick up oddball items at the grocery store or anywhere else. A recent update also allows you to set up recurring notifications for when you need to get into the habit of something. Checkmark's on sale for today only, so grab it for free while you can.